A rotational driving force imparting device includes an electric motor device that generates a rotational driving force, and a transmission device that changes the rotational driving force generated in the electric motor device and transmits the changed rotational driving force to the driving target.
Patent Document 1 below discloses the rotational driving force imparting device as described above. The transmission device of the rotational driving force imparting device is a planetary gear transmission device. This transmission device includes a sun gear that rotates about a shaft line, a plurality of planetary gears that revolve about the shaft line in engagement with the sun gear and rotate about their own center line, an arm or a carrier that supports the plurality of planetary gears, and an internal gear in which a plurality of teeth are aligned annularly about the shaft line and are engaged with the planetary gears. An arm shaft extending in an axial direction about a shaft line is fixed to the arm. This arm shaft forms an output shaft that is connected to a driving target.
The electric motor device of this rotational driving force imparting device includes an auxiliary motor that rotates the sun gear about the shaft line, a transfer mechanism that transfers a rotational driving force of the auxiliary motor to the sun gear, a main motor that rotates the internal gear about the shaft line, and a transfer mechanism that transfers a rotational driving force of the main motor to the internal gear. A rotor shaft of the auxiliary motor and a rotor shaft of the main motor are both arranged at a position to the shaft line of the transmission device and separate in the radial direction from the shaft line. Each transfer mechanism includes a belt and a pulley.
In this rotational driving force imparting device, a rotational speedrotational speed of an output shaft connected to a driving target can be changed by changing a rotational speedrotational speed of the auxiliary motor.